Mechanical Properties of the Composites

Composite Nanotube type Nanotube cont. PVA mol weight Y/Y p g/g p Reference 

Film Catal. MWNT 1 wt% 5 wt% 30000-70000 5.8 Loss 1.9 Loss Ryan 07 

Raw gel-spun fiber HipCo SWNT in DMSO 3 wt% 200000 1.4 1.2 Zhang 04 

Hot-stretched wet-spun fibers HipCo SWNT, MWNT, (SDS) 30 wt% 195000 6.5 Miaudet 05 

Nanotube functionalization is performed in other examples listed in Table 11.1. In 1999, Shaffer et al. used carboxylated MWNTs. By contrast to studies described in the followings, this allows to the achievement of homogeneous composites with a large nanotube fraction of about 50 wt%. However, the improvement of the Young s modulus is still weak, particularly if we consider the large amount of CNTs included in the matrix. Liu et al. (47) reported an improvement of mechanical properties with SWNTs which are covalently functionalized by OH groups, compared to the same neat nanotubes simply dispersed with SDS. 

---

The above data represent the first from composites fabricated with fixed catalyst VGCF. A review of the data leads to the conclusion that the thermal and electrical properties of this type of carbon fiber are perhaps the most likely to be exploited in the short term. While mechanical properties of the composites are not as attractive as the thermal and electrical, it may be noted that no effort has... 

Lee [242] studied the dependence of the physico-mechanical properties of Wollastonite-filled polychloroprene rubber on the type of agent used to pre-treat the filler. The composition contained 26.9 part (weight) of the filler per 100 parts (weight) of the rubber (compositions CR-1100, CR-174, CR-151). The finishing agents were y-aminopropyl triethoxysilane (CR-1100 and CR-174) and vinyl triethoxysilane (CR-151). The mechanical properties of the compositions are listed in Table 7 below. The author proposed an empirical equation to relate the modulus with the equilibrium work of adhesion in the following form ... 

Thus, bearing in mind that smaller filler concentrations worsen the physical-mechanical properties of the composites to a smaller degree, it follows that the most promising are the fillers which provide for a preset level of a at smaller concentration. The table shows that the most promising are carbon fibers coated with Ni (American Cyanamid) and steel fibers (Brunswick Corp.) [16]. 

The values of Oj s together with the respective values for the moduli of the composites Ec were introduced in the adequate models expressing the mechanical properties of the composites in terms of their constituents, and gave excellent coincidence with their experimental values based on the cubic variation of ir with of. The values of the characteristic quantities for the three-term unfolding model, as derived from the above-described procedure, are all included in Table 1. 

In this section, we discuss theoretically the influence of microscopic interaction between polarized particles on the macroscopic mechanical properties of the composite gel, in particular, the elastic modulus. 

Some satisfactory results were also obtained by modification of properties of phenol-formaldehyde resin (PFR) composites with the synthesized diallylsilazanes (scheme 1). Thas, addition of diallylsilazanes (1-3 mass %) to this composition has improved some of essential characteristics of hardened PFR (table 3). It should be noted that other important physical and mechanical properties of the composites have remained safe (table 3). 

Apart from the mechanical properties of the composite constituents that dominate the fiber fragment length, peculiar structural properties of the fiber may... 

The interfacial characteristics can be optimized by the application of appropriate coatings to the fiber, allowing desired mechanical properties of the composites to be... 

A candidate interlayer consisting of dual coatings of Cu and Nb has been identified successfully for the SiC-Ti3Al-I-Nb composite system. The predicted residual thermal stresses resulting from a stress free temperature to room temperature (with AT = —774°C) for the composites with and without the interlayers are illustrated in Fig. 7.23. The thermo-mechanical properties of the composite constituents used for the calculation are given in Table 7.5. A number of observations can be made about the benefits gained due to the presence of the interlayer. Reductions in both the radial, and circumferential, o-p, stress components within the fiber and matrix are significant, whereas a moderate increase in the axial stress component, chemical compatibility of Cu with the fiber and matrix materials has been closely examined by Misra (1991). 

Thermal changes within the range to which restoratives may be exposed in the mount, 0 -60 °C, may have other effects on the composite restorative. It is possible that these changes can cause decreases in the mechanical properties of the composites [255-257]. These temperatures may approach the glass transition temperatures of some of the less densely crosslinked resin systems used, increasing the negative impact on the mechanical properties. 

As mentioned in the introduction to the section on composites, the interphase, or the region between the matrix and the reinforcement, is often the primary determinant of mechanical properties of the composite. It can have an effect on other properties as well, but since it serves to transfer loads from the matrix to the reinforcement, its primary impact is on the strength of the composite. 

Although a number of filler characteristics influence composite properties, particle size, specific surface area, and surface energetics must again be mentioned here. All three also influence interfacial interactions. In the case of large particles and weak adhesion, the separation of the matrix/ filler interface is easy, debonding takes place under the effect of a small external load. Small particles form aggregates which cause a deterioration in the mechanical properties of the composites. Specific surface area, which depends on the particle size distribution of the filler, determines the size of the contact surface between the polymer and the filler. The size of this surface plays a crucial role in interfacial interactions and the formation of the interphase. 

It has also been suggested that steady state low shear dynamic measurements in the melt could be a convenient method for the study of particle dispersion in relation to flller properties, which might also correlate with mechanical properties of the composite [48,49]. 

The purpose of the second dwell is to allow crosslinking of the matrix to take place. It is during the second dwell when the strength and related mechanical properties of the composite are developed. To characterize the exothermic crosslinking reaction of a thermosetting polymer matrix, a thermal cure monitor technique such as Differential Scanning Calorimetry... 

We focus here on the polystyrene/high-density polyethylene (HDPE) system. We have studied this system in greater detail than any other and describe here the phase behavior of this system, the blend synthesis, and some mechanical properties of the composites. 

In this chapter, we describe the synthesis and characterisation of the microstructure and properties of layered-graded alumina-matrix composites through liquid infiltration. This approach is relatively simple and offers excellent control over the depth of the graded layer. The presence of a graded dispersion of reinforced particles in the alumina matrix has a profound influence on the physical and mechanical properties of the composites. An overview of the infiltration kinetics and the use of the infiltration process as a new philosophy for tailoring novel graded ceramic systems are also presented. 

The main function of the resin is, to provide an even stress distribution over the fibres. The mechanical properties of the composite depend, in the first place, on the amount of glass and on its distribution over the matrix. 

---